A Quantum Cascade Laser (QCL) is known as a light source in the mid-infrared region of wavelengths of about 5 to 30 μm (e.g., cf. Patent Literature 1). The quantum cascade laser is a monopolar type device making use of electron transitions between subbands created in semiconductor quantum wells. The quantum cascade laser implements high-efficiency and high-output operation by cascade coupling of a stack of multiple active layers of semiconductor quantum well structure. Currently, continuous wave (CW) operation is achieved at room temperature (RT) in the wide wavelength band of 3.8 to 11.5 μm and examples of the quantum cascade lasers in practical use include pulse operation type quantum cascade lasers and CW (Continuous Wave) operation type quantum cascade lasers.